Skin protection conditioned after sunbathing skin cancer

Study: The anti-UV skin pigment melanin could be involved in the development of skin cancer

02/20/2015

When the first warming sunrays appear in spring, it attracts many people into the open air. After the long, gray autumn and winter, the sun can be a real treat for the soul. In addition, it stimulates vitamin D production in the skin, which benefits the immune system and bone formation in particular. Unfortunately, UV radiation also has a negative effect: People who frequently expose themselves to intense sunlight have an increased risk of skin cancer. So far, experts have assumed that the pigment melanin in the skin provides a - albeit limited - natural protection against damage from UV radiation. Researchers led by Douglas Brash of New Haven's Yale School of Medicine, however, have recently discovered that melanin has another effect related to solar radiation. According to their study results, in the journal „Science“ were published, threatens damage to the genome in the melanin-forming cells for hours after sunbathing.

Melanin provides skin protection and can also cause skin cancer
The pigment melanin gives the skin, the choroid and the hair its black-brown or reddish color. The dye is intensified by sunlight and provides a natural protection against damage from UV radiation. Therefore, populations that are more pigmented with high levels of eumelanin are less likely to develop skin cancer. The protective effect of melanin is based on a process whereby the pigment converts a large portion of the radiant energy into harmless heat, thereby preventing DNA damage to the skin cells.

Brash and his team wanted to investigate the exact mechanisms that occur in the melanin-producing cells. They created cell cultures with melanocytes (pigment cells) from mice and humans and exposed them to UV-A light. As expected, so-called cyclobutane dimers (CPDs) were formed. Two specific adjacent DNA building blocks connect so that the DNA strand can no longer be read correctly. As a result, the cell dies. However, it can also develop skin cancer. Normally, CPDs occur within picoseconds. In the researchers' experiments, however, the melanocytes also formed CPDs up to three hours after UV irradiation. For other skin cells, however, this process stopped as soon as the radiation was no longer present. The conclusion of the researchers: Melanin not only has protective effects, but can also trigger carcinogenic processes. This applies especially to the lighter phaeomelanin, which dominates redheads, the researchers report in the journal.

UV radiation initiates cancer-causing processes in melanin-producing cells
Further experiments with mouse cells, in which the repair processes of the cells were suppressed, showed that about half of all recorded CPDs were formed only after the end of the UV irradiation. The light causes an activation avalanche, which ultimately leads to the excitation of an electron of melanin. In the further course, the energy surplus is transferred to the genome and cause the same damage there as under the influence of sunlight.

„That means we underestimated the extent of DNA damage people get from UV exposure, "Brash cites in a note from the journal. „If we could divert the energy from the excited melanin before it is transmitted, we would be able to intervene.“ In the study, the researchers found that a vitamin E lotion can reduce the delayed effects of UV radiation, which only occurs in the dark. But they also point out that there might be other compounds that work even better.

„Looking at data on currently available sunscreen and skin cancer prevention, it's not great, "says dermatologist David Fisher of the Massachusetts General Hospital in Boston, who was not involved in the study, to the trade magazine. „But these new insights could give us new ways to improve this. "

Addicted to sunbathing
A study by researchers around David Fisher of the Massachusetts General Hospital in Boston, which featured in the journal last June „Cell "came to the conclusion that sunbathing is addictive, which could explain why many people despite the knowledge of the dangers of UV radiation still regularly - sometimes even without sunscreen - the intense sun exposure or go to the solarium.

As part of their research, the researchers regularly expose mice to UV radiation for several weeks. As a result, more endorphins, body-related painkillers, were released. In the next step, the researchers blocked the effect of endorphins by drugs. The mice responded with classic withdrawal symptoms such as tremors, and teeth chattering. The scientists suggest that the urge for sun could be related to vitamin D levels.